FIELD OF THE INVENTION
This invention relates to digital computer systems, and especially to methods and apparatus for distinguishing between data words that may otherwise be identical in terms of their physical origins, for such purposes as protecting against the unauthorized entry of data into a computer through communications lines, this particular purpose being especially directed towards methods and apparatus for discriminating between remote data and data that have been generated locally as by a keyboard or mouse or the like. Related apparatus and methods of authenticating digital data control local access to selected computer peripherals.